A couple of years ago, at the peak of my children's reluctance to eat vegetables, I decided to try an experiment.
When the kids arrived home from daycare one afternoon, I had bowls of colorful vegetables cut up and ready to go: crunchy red and yellow peppers, bushy little florets of broccoli, tomatoes and mushrooms and olives. I gave them each a cheese pizza base to "decorate" for dinner, and they gleefully complied. My older daughter made a face with olive eyes, broccoli hair, and a bright, red-pepper mouth. My younger daughter loaded on veggies by the fistful.
It felt like a parenting win! And I smugly patted myself on the back as the pizzas cooked in the oven, as we inhaled that toasty pizza smell, and as we sat down to eat. And I kept patting myself on the back right until the moment the freshly-baked pizzas made it back to their creators, who both — without hesitation — removed every speck of vegetable matter before happily consuming the "just cheese pizza" left behind.
As an effort to increase vegetable consumption, my experiment was not a success. And yet, I'd been motivated by a compelling idea — the idea that we value something more highly when we make it ourselves.
A 2012 paper dubbed this phenomenon "the IKEA effect," and demonstrated that adults who successfully completed tasks, such as assembling IKEA boxes or folding origami, valued the completed products more highly than equivalent products that they did not create themselves. Subsequent studies have demonstrated the same sorts of effects across a variety of contexts, including product customization, LEGO constructions, and even food preparation. So why was my well-intentioned vegetable experiment such a decisive failure?
A new paper, published this month in the journal Cognition, offers a possible answer. And that answer has to do with development. Just as our basic social, emotional, and cognitive abilities develop throughout childhood, so do the factors that eventually give rise to an IKEA effect in adulthood. It wasn't (only) that my two young daughters (really) didn't want to eat those vegetables — it was also that they were too young to exhibit an IKEA effect.
The new paper, authored by experimental psychologists Lauren Marsh, Patricia Kanngiesser, and Bruce Hood, reports an initial experiment in which 64 children aged 3 to 6 were given the opportunity to interact with two foam "monsters" — one that they created themselves by following instructions from a kit, and another that they merely held on to while playing a short game. As a result, both monsters were equally familiar to the children, but only the former had been self-created.
Before creating or holding either monster, the experimenters had each child rate how much she liked each monster, either rating a monster identical to the monster about to be created, or rating the monster the child would go on to hold. These ratings were repeated after creating or holding a monster, so the researchers could assess how much each monster's perceived value was affected by the preceding interaction. If children value objects more highly just because they successfully create the objects themselves — in other words, if kids show an IKEA effect — then we'd expect kids' ratings to increase more for the monster they created than for the monster they just held. And this is precisely what the researchers found, but only for the 5- and 6-year-olds. The 3- and 4-year-olds showed no such effect.
This finding suggests that something changes around age 4 or 5 such that children begin to exhibit an adult-like IKEA effect. But what might that be?
Different accounts of what drives the IKEA effect suggest different answers. One possibility is that the IKEA effect results from the effort that creation requires: When we invest more effort in something, we typically come to value it more highly. Other possibilities are that we value things more highly when we feel ownership over them, or when we think they signal something positive about our own skill or competence. It could be that between ages 4 and 5, children come to appreciate these aspects of effort, ownership, or signaled competence.
Across two subsequent studies, the researchers aimed to test these possibilities by varying different features of the experiments, including whether creating the monster required lower or higher levels of effort, whether the created monster was or wasn't owned by the child, and whether the finished monster would be displayed in a public location. These factors didn't have any reliable effects on the 5- and 6-year-old participants' ratings of how much they valued the monsters, even though the children did, on average, show an IKEA effect. This provides some evidence against the idea that these factors are what drives the IKEA effect, at least in young children.
So what was driving the IKEA effect in these young kids? It's always possible that effort, ownership, or signaled competence really do make a difference, but that the experiments didn't manipulate or measure the effects of these factors in an effective way. But another possibility is that current accounts of the IKEA effect are inaccurate or incomplete. Marsh and colleagues have their own proposal, motivated by the sense of self that children develop around this age: that beginning around age 5, children come to value their own creations because they "become part of who we are, a tangible manifestation of self." In other words, we value what we create ourselves because it becomes an extension of our self and identity.
If Marsh and colleagues are right that the IKEA effect emerges around age 5, then my pizza experiment may have failed because my children were simply too young. But it's also possible that vegetables present their own challenges. Perhaps its harder to make vegetables seem like "a tangible manifestation of self" compared to a more highly valued commodity, like furniture — or a foam monster.
In fact, a 2017 paper reports an experiment very much like mine, only with a slightly larger sample size — and ever so slightly better experimental control. In the experiment, 86 children aged 4 to 6 were shown a "peacock" with feathers made of vegetables. Half the kids then had an opportunity to make a vegetable peacock themselves, and half to make a similar peacock using beads. The researchers subsequently provided each child with a vegetable peacock (either the one they just made or one that was made for them), as well as additional veggies, and they measured how many pieces of vegetables the kids in each group ate.
The bad news is that creating the veggie peacock didn't have a significant effect on vegetable consumption. The good news is that vegetable consumption wasn't too bad: the kids, on average, consumed over 17 pieces of vegetables each, whether or not they made their own veggie peacock. It's possible the veggie peacock itself was an inducement to consume, and that self-crafting didn't have an additional effect because the kids were still fairly young. It's also possible that the IKEA effect is more likely to show up for a high status or highly desirable object — like a milkshake — than for a cucumber.
But I'm not ready to give up on vegetables yet. A 2014 paper reports a finding from an experiment with 47 children aged 6 to 10: When the children were involved in meal preparation, they ate more salad from those meals. A handful of other papers report positive associations between involvement in food preparation (whether it's gardening or cooking) and food consumption — but others report no effects at all.
Clearly, many questions remain about the IKEA effect, about how it develops, about how it manifests in the case of food, and about the ever-pressing question of how to get children to eat more veggies. Hopefully, new studies will bring some clear and useful answers. But in the meantime, now that my kids are older, I'm going to give the vegetable pizza experiment another go. And as a side dish, we'll have some veggie peacocks.
Tania Lombrozo is a psychology professor at the University of California, Berkeley. She writes about psychology, cognitive science and philosophy, with occasional forays into parenting and veganism. You can keep up with more of what she is thinking on Twitter: @TaniaLombrozo